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Cold Frames: A Year Round Gardening Tool

Give your garden plants a head-start and shelter from chilly spring weather with a versatile cold frame.

Cold Frame GardeningSpringtime sees your friendly, think-ahead Planet Natural blogger using cold frames heavily. Now, in a time of year where frosts are still possible, many of our indoor vegetable starts are almost ready to go into the garden. They need to get use to being outdoors. Many of them can’t survive the night-time cold but can when protected inside a cold frame, maybe draped with a blanket on the coldest nights.

It’s also the time of year we’ve also run out of room under our indoor grow light and need a place to keep vegetable starts where they’ll get more sunshine than they would on a window sill. And we also want to get a head start on some of our long-season plants, like tomatoes, peppers or winter squash.

Can you see why we’re thinking a second, and maybe a third, cold frame might be a good — make that great — idea?

And don’t forget flowering plants. You can get a big jump growing pansies by starting them in pots inside a cold frame.

Get off to a fast start with the Poly-Tex® Double Cold Frame! Easy-to-assemble and gives the protection you need when starting plants early or protecting late into the season. Includes two adjustable top doors for easy venting and access.

But cold frames aren’t just an amazing accessory to your springtime gardening. They’re good for a number of uses year ’round:

  1. Storing potted plants and cold-sensitive bulbs and root-cuttings (buried in sawdust or straw) during winters in areas where night-time temperatures aren’t consistently extreme (near and below zero).
  2. Late fall plantings of such cold hardy plants as broccoli, kale, and spinach can be overwintered in a cold frame — plant them right in the ground –and can even provide early spring and mid-winter harvests during warm spells. Fresh greens in February? Yeah!
  3. Start vegetable seeds in pots ahead of gardening season.
  4. Hardening off your vegetable starts as they provide warmth (even with the tops up), protect against excess wind, and offer warmer overnight temperatures.
  5. Sow squash seed or set out tomato plants once there’s room. They’ll give these long season vegetables a warm, jump start. By the time they’re pushing up against the cold frame’s top, just leave the tops off.
  6. Plant greens in late summer and hold them well past the first frosts of fall…and maybe longer.

You may have other uses for your cold frame. Let’s us know, either by leaving a comment below or on our Facebook page.

When locating a permanently-placed cold frame, make sure the soil drainage is good. This might require digging up the soil to a depth of two or three feet and putting in a six-inch layer of pea-gravel or small river rock to facilitate water conduction before laying down compost and soil. If you’re only using a cold frame for potted plants and starts, you can just dig up six inches of soil and add a gravel surface. The gravel or tile or stone will serve as a heat sink, carrying the day’s accumulated warmth into the night. We’ve seen gardeners set concrete blocks in sideways, then fill the spaces with gravel to provide a heat-retaining surface.

Placing your permanent cold frame against the south or west-facing side of a building will also help it gather and retain heat. The building will also provide shelter from the wind. Here’s examples of permanent cold frames (brick!) incorporated into the sides of buildings. Ours was against a white garage wall which gave the tomatoes we grew there and extra warm and sunny boost throughout the summer, just what they needed in short-season Montana.

Covering your raised garden bed with plastic or some other type of light-conducting shelter can turn it into a wonderful cold frame.

Cold frames that sit on top of the soil and are moveable can travel from place to place as you plant different, heat-loving vegetables. You can build one that’s transportable or construct a makeshift one of hay bales, which are especially good insulators, by placing them in a square or rectangle just big enough to support old window frames with glass or shower door. They’re also available as kits and can even be made of convenient materials that make them lightweight and functional as tents.

You can turn your cold frame into a hot box by adding rotting manure or a layer of leaves or straw seasoned with microbe-rich compost beneath your soil layer. The heat generated by the decaying organic material will help hold plants over winter as well as give soil temperatures a boost in time for spring germination. One gardener we know reported great result using a layer of alfalfa pellets and some compost instead of straw or leaves (which tend to compact…chop them first).

Here’s a comprehensive cold frame guide — with building plans — from the University of Missouri. We’d really like to hear about your cold frame — how it’s built, where it’s located, how you use it. And you can post pictures — we’d love to see them! — at Facebook or at the Planet Natural Twitter page #coldframes.

One warning about cold frames . . . they can get hot when the sun’s shining! Be sure to ventilate them by lifting the lids and propping open — or removing the lids all together — on sunny days. It’s an unpleasant surprise to come home from work at the end of the day and find your lettuce starts baked beneath the glass or plastic.

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